Batteries powered by bacteria could prove highly useful in offering spurts of electricity where it isn't readily available, maybe running low-energy diagnostic devices in the developing world, for example. Seokheun Choi, a Computer Science Assistant at Binghamton University, has been investigating these possibilities over the last five years, developing origami-style and ninja-star-like paper batteries that are powered by dirty water. His latest breakthrough battery design calls only on bodily fluids, and was able to power an LED light using a single drop of spit.

These types of bacteria-based batteries rely on what are known as microbial fuel cells (MFCs). These cells use bacteria to carry out reduction/oxidation reactions, which swap electrons between molecules to produce electricity. We have seen this process fuelled by dirty water, in the examples mentioned above, but also urine and now saliva too.

For his latest paper-based battery, Choi uses MFCs built from inactive, freeze-dried exoelectrogenic cells, which can be kept for long periods and generate power within minutes of adding saliva.

"Freeze-drying technique is to store the bacterial cells in the device for a long-term period," he explains to New Atlas. "Bacterial electricity has long been studied. During their respiration by consuming organic materials like saliva, bacteria can transfer electrons to the external electrode."

In testing the device, the team was able to achieve a power density of a few microwatts per square centimeter, enough to turn on an LED light. Eventually, it hopes the device can be used to power disposable diagnostic devices in developing countries, which require tens of microwatt-level power for several minutes at a time. Choi is now working to improve the power density further to open up even more possibilities, which he tells us can be achieved by "folding or stacking devices fabricated on a single sheet of paper."